As the present society ages, it is anticipated that there will be an increase in adverse spinal conditions which are characteristic of older people. Certain biochemical changes can occur with aging, affecting tissue found throughout the body. In the spine, the structure of the intervertebral disks can be compromised, in part as the structure of the annulus fibrosus of the intervertebral disk weakens due to degenerative effects. Spondylosis (also referred to as spinal osteoarthritis) is one example of a degenerative disorder that can cause loss of normal spinal structure and function. The degenerative process can impact the cervical, thoracic, and/or lumbar regions of the spine, affecting the intervertebral disks and the facet joints. Pain associated with degenerative disorders is often triggered by one or both of forward flexion and hyperextension. Spondylosis in the thoracic region of the spine can cause disk pain during flexion and facet pain during hyperextension. Spondylosis can affect the lumbar region of the spine, which carries most of the body's weight, and movement can stimulate pain fibers in the annulus fibrosus and facet joints.
Over time, loss of disk height can result in a degenerative cascade with deterioration of all components of the motion segment resulting in segment instability and ultimately in spinal stenosis (including, but not limited to, central canal and lateral stenosis). Spinal stenosis results in a reduction in foraminal area (i.e., the available space for the passage of nerves and blood vessels) which compresses the nerve roots and causes radicular pain. Another symptom of spinal stenosis is myelopathy. Extension and ipsilateral rotation further reduces the foraminal area and contributes to pain, nerve root compression and neural injury. During the process of deterioration, disks can become herniated and/or become internally torn and chronically painful. When symptoms seem to emanate from both anterior (disk) and posterior (facets and foramen) structures, patients cannot tolerate positions of extension or flexion.
A common procedure for handling pain associated with degenerative spinal disk disease is the use of devices for fusing together two or more adjacent vertebral bodies. The procedure is known by a number of terms, one of which is interbody fusion. Interbody fusion can be accomplished through the use of a number of devices and methods known in the art. These include screw arrangements, solid bone implant methodologies, and fusion devices which include a cage or other mechanism which is packed with bone and/or bone growth inducing substances. All of the above are implanted between adjacent vertebral bodies in order to fuse the vertebral bodies together, alleviating associated pain.
Depending on the degree of slip and other factors, a physician may fuse the vertebra “as is,” or fuse the vertebrae and also use a supplemental device. Supplemental devices are often associated with primary fusion devices and methods, and assist in the fusion process. Supplemental devices assist during the several month period when bone from the adjacent vertebral bodies is growing together through the primary fusion device in order to fuse the adjacent vertebral bodies. During this period it is advantageous to have the vertebral bodies held immobile with respect to each other so that sufficient bone growth can be established. Supplemental devices can include hook and rod arrangements, screw arrangements, and a number of other devices which include straps, wires, and bands, all of which are used to immobilize one portion of the spine relative to another. Supplemental devices have the disadvantage that they generally require extensive surgical procedures in addition to the extensive procedure surrounding the primary fusion implant. Such extensive surgical procedures include additional risks, including risk of causing damage to the spinal nerves during implantation. Spinal fusion can include highly invasive surgery requiring use of a general anesthetic, which itself includes additional risks. Risks further include the possibility of infection, and extensive trauma and damage to the bone of the vertebrae caused either by anchoring of the primary fusion device or the supplemental device. Finally, spinal fusion can result in an absolute loss of relative movement between vertebral bodies.
U.S. Pat. No. 5,496,318 to Howland, et al. teaches supplemental devices for the stabilization of the spine for use with surgical procedures to implant a primary fusion device. Howland '318 teaches an H-shaped spacer having two pieces held together by a belt, steel cable, or polytetrafluoroethane web material, one or both ends of which includes an attachment device fixedly connected with the respective end. Howland '318 teaches that the vertebra are preferably surgically modified to include a square notch to locate the fixation device in a preferred location. Howland '318 has the further disadvantage that the belt, cable or web material must be sized before implantation, increasing the procedure time to include sizing time and reducing the precision of the fit where both ends of the belt, cable or web material include attachment devices (and as such are incrementally sized).
U.S. Pat. No. 5,609,634 to Voydeville teaches a prosthesis including a semi-flexible interspinous block positioned between adjacent spinous processes and a ligament made from the same material. A physician must lace the ligament through the interspinous block and around the spinous processes in a figure of eight, through the interspinous block and around the spinous processes in an oval, and suture the ligament to itself to fix the interspinous block in place. Voydeville has the disadvantage of requiring significant displacement and/or removal of tissue associated with the spinous processes, potentially resulting in significant trauma and damage. Voydeville has the further disadvantage of requiring the physician to lace the interspinous ligament through the interspinous block. Such a procedure can require care and time, particularly because a physician's ability to view the area of interest is complicated by suffusion of blood in the area of interest.
It would be advantageous if a device and procedure for limiting flexion and extension of adjacent vertebral bodies were as simple and easy to perform as possible, and would preferably (though not necessarily) leave intact all bone, ligament, and other tissue which comprise and surround the spine. Accordingly, there is a need for procedures and implants which are minimally invasive and which can supplement or substitute for primary fusion devices and methods, or other spine fixation devices and methods. Accordingly, a need exists to develop spine implants that alleviate pain caused by spinal stenosis and other such conditions caused by damage to, or degeneration of, the spine. Such implants would distract (increase) or maintain the space between the vertebrae to increase the foraminal area and reduce pressure on the nerves and blood vessels of the spine, and limit or block flexion to reduce pain resulting from spondylosis and other such degenerative conditions.
A further need exists for development of a minimally invasive surgical implantation method for spine implants that preserves the physiology of the spine. A still further need exists for an implant that accommodates the distinct anatomical structures of the spine, minimizes further trauma to the spine, and obviates the need for invasive methods of surgical implantation. Additionally, a need exists to address adverse spinal conditions that are exacerbated by spinal extension and flexion.